Support publishing to NPM

[halfmatthalfcat]

To better support publish workflows, it'd be nice to create a task to publish to the npm registry defined in the outputted package.json. I started work on the npm-publish branch, but it's a mess of SbtWeb, SbtJsEngine and other craziness to get it to work.

For now, I'm going to simply npm link for local development and, in a CI/CD context, just move the compiled codebase into an npm container and cd+npm publish from within target/typescript directly.